Cathode-ray tube with spot intensity proportional to radial deflection



' Feb. M 1947.

G. W. NAGEL CATHODE RAY TUBE WITH SPOT INTENSITY PROPORTIONAL T0 RADIALDEFLECTION Filed NOV. 24, 1943 vi & 2

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ATTORN Patented Feb. 18, 1947 CATHODE-RAY TUBE WITH SPOT 1N- TENSITYPROPORTIONAL TO RADIAL DEFLECTION George W. Nagel, Baltimore, Md.,assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., acorporation of Pennsylvania Application November 24, 1943, Serial No.511m 3 Claims.

My invention relates to cathode ray tubes and, In particular, to suchtubes in which the incidence of an electron beam on a screen on the endof the tube produces a luminous spot which is caused to scan, byrepeated radial movements, the entire circular end of the tube.

For certain purposes, notably in connection with the present war work,cathode ray tubes are used in which the electron beam by repeated radialmovements from the center to the circumference scans the entire circulararea forming the luminous screen at the end of the tube The successiveradial movements from center to periphery are displaced slightly'in anangular direction from each other, this displacement being such that theadjacent edges of successive radial paths touch each other at theperiphery of the screen so that after the entire 360 of circumferencehas been traversed there are no areas which have not been swept over bythe moving spot. However, a moment's consideration will make it evidentthat successive paths must over lap each other at all radial distancesexcept at the very periphery of the screen under the conditions justoutlined. Since the luminous effect itself persists for an intervalafter the cathode ray has once left a given elementary area on thescreen, this repeated traverse by the luminous spot of areas in thecentral portion of the screen gives such areas a greater specificluminous intensity than is attained by similar areas at the periphery ofthe screen. In other words, the can tral portions of the screen appearmuch brighter than the peripheral portions, and this effect may beintensified by the well known phenomenon of persistence of human vision.

One object or my invention is, accordingly, to provide a cathode raytube in which the luminous screen is scanned by radial movements of thesort above described but in whichthe luminous intensity is made uniformthroughout the area of the screen. l

Another object of my invention is to produce a cathode ray tube having aluminous screen subject to radial scansion in which the intensity ofelectron bombardment of the screen varies inversely with the radialdistance from the center of the screen. I

Other objects of my invention will become apparent upon reading thefollowing description taken in connection with the drawing, in which:

Figure 1 is a schematic diagram of the electrical circuits of a cathoderay tube embodying the principles of my invention; and l Figure 2 is agraph illustrating the variation intimeof s erms voltage used incarrying out my invention. l l U A Referring in detail to Fig. 1, item[is a cathode ray tube which comp rises a vacuum-tight tube having arelatively long cylindrical neck portion a which expands at one end toform a circular screen 3, The screen end of the tube is coated on itsinterior surface with willinanite or other material which isr'enderedluminous when loombar ded by electrons. In the other end of the tube ispositioned an electron-gun of a type well known in the art comprising anelectron emissive surface, and a virtual cathode '4 of small areaassociated with cylindrical anodes 5 and "Iii through which electronsare projectedin a fine stream along the axis oi the tube I. The cathode4, nd anodes 5 and Ill, may respectively be en e'rgize'd from a highvolta'g'e power supply 6 in which the positive tei'minal is preferablyground ed and the negative terminal connected to the cathode '4. Infront of the cathode 4 is located a control electrode 7 through whichthe abovementioned electron stream is projected. The control electrode 1maybe connected through a' resistor 8 to a bias battery 1 which makes itsomewhat more negative than the cathode. Bee tween the anode l0 and theluminous screen 3 the electron stream passes through the fields of apair of deflecting magnets 53 of a type Well known in the art whichproduces a magnetic field trans- Verse to the central axis of the tubeI. Such a magnetic field will act upon the electrons travelling alongthe central axis of the tube l to give them a radial velocity componentwhich lies in a plane passing through the central axis of the tube lnormal to the direction of the transverse magnetic field abovementioned. The amountof the radial acceleration producing this velocitywill be proportional at any. instant to the strength of the transversemagnetic field. Thus, if the direction of the magnetic field were fixedand invariable, and a constantly increasing current were to provide auniform increase with time of the transverse magnetic field, the pointof incidenc'e on the screen 3 of the electron stream would be iiiovedradially outward uniformly from the center totheperiphery of the screen3. As will be described in more detail below, the tubes ll, [2 and isconstitute an electrical generator which causes the transverse magneticfield above mentioned to rise gradually from zero to a maximum at auniform' rate in each of a series of successive cycles. J} v In orderthat the" radial movements of the spot of incidence of the electron beamon screen 3 shall gradually traverse the entire area of the screen, themagnetic system above mentioned is arranged to be rotated in a planeperpendicular to the axis of the tube I by an electric motor l4. As aresult of this rotation the annular position about said axis in whichthe electron beam is deflected continually changes at a rate which issmall compared to the period of radial movement itself. The relation ofthe rate of rotation of the motor I4 and the periodicity of the voltagefrom generator II, I2, I3 is made such that between successive outwardsweeps of the electron beam it has moved an angular distance at theperiphery at the screen 3 which is substantially equal to the width in acircumferential direction of the luminous spot.

The wave form of the voltage impressed by the generator II, I2, I3 onthe windings producing the transverse magnetic field above mentioned issubstantially similar to that shown in Fig. 2. At the beginning of eachperiod this voltage rises rapidly to a certain value and thereafterincreases uniformly with the time to a maximum value, whereupon it fallsrapidly to its original value and so continues until the beginning of asecond cycle.

The generator II, I2, I3 comprises an output tube I I of any suitabletype embodying an anode, control electrode and a cathode. The cathode isconnected through a resistor I5 to the positive terminal of a biasbattery I6 of which the negative terminal is connected to ground. Thecathode of the tube II is likewise connected through a capacitor H toone terminal of the windings 9 producing the above-mentioned transversemagnetic field, the other terminal of the windings 9 being grounded. Theanode of the tube II is connected to a suitable source of positivedirect currentpotential of which the negative terminal is connected toground. The control electrode of the tube II is connected through aresistor I8 and a capacitor I9 to ground. The same control electrode islikewise connected to the anode of the tube I2. The tubes I2 and I3constitute what is frequently referred to as a multivibrator. The anodeof the tube I2 is connected through a resistor to the positive terminalof a suitable voltage source of which the negative terminal is grounded.The cathode of the tube I2 is connected through a resistor 2I to ground.The control electrode of the tube I2 is connected through a capacitor 22to the anode of the tube I3 and is also connected through a resistor 23to ground. The anode of the tube I3 is connected through a resistor tothe positive terminal of a suitable voltage source of which the negativeterminal is grounded. The cathode of the tube I3 is connected directlyin parallel with the cathode of the tube I2. The control electrode ofthe tube I3 is connected to the negative terminal of a suitable biasingvoltage sourc 24 of which the positive terminal is connected to ground.

The arrangement so far disclosed would produce the type of luminosity onthe screen 3 which is conventional in the prior art; namely, theluminous intensity on the screen would be roughly inversely proportionalto the radial deflection.

In practical use of tubes of the type so far described, it is customaryto impress varying voltages on the control electrode I of the tube I toproduce luminous patterns thereon which are indicative of certainquantities or measurements which it is desired to observe. If, however,the variations of intensity over the screen are to be III 4 trulyrepresentative of the variations in intensity of the quantity beingobserved, it is essential that the luminous intensity of the screenshall be free from variation in accordance with radial distance or anyother quantity not related to the quantity being observed. For thisreason, a screen in which the luminous intensity is free from variationin accordance with radial distance is a great improvement over thepresent conventional type of screen.

In accordance with my invention, the quantity which is to undergoobservation by producing luminous patterns on the screen 3 is impressedon an input circuit having one terminal 25 connected through a condenser2'! to the control electrode 28 of an amplifier tube 29, the otherterminal 3| of the input circuit being connected to ground. The tube 29is preferably a remote cut-off type pentode, the gain of which increasesas its grid bias is made less negative. The cathode of the tube 29 isconnected to ground through a resistor 32 shunted by a capacitor 33 andis likewise connected to a suppressor electrode 34 of the tube 29. Ascreen electrode 35 of the tube 29 is connected to one terminal of asource of suitable positive voltage of which the negative terminal isgrounded. The positive terminal of the above-mentioned source islikewise connected through a resistor 36 to the anode of the tube 29.The anode of the tube 29 is connected through a capacitor 31 to thecontrol electrode 1 of the cathode ray tube I.

In order to so modulate the intensity of the cathode ray beam reachingthe screen 3 as to reduced the luminous intensity in the radially inwardportion of the screen and to produce uniform luminosity throughout thearea of the screen, a portion of the output voltage of the resistor I5of the tube II which supplies the energy of the magnetic field isconnected through a suitable capacitor 38 to the control electrode 28 ofthe tube 29. The magnitudes of the resistor 32 and of the voltageimpressed on the electrode 28 of tube 29, when the voltage impressedacross the terminal 25-3l is zero, are adjusted to such a value that thevoltage impressed on the control electrode of tube 2 is so low duringthe troughs of the voltage waves shown in Fig. 2 that no electrons fromthe cathode I strike the screen 3 with sufficient velocity to form aluminous spot thereon. When the voltage of Fig. 2 rises sufiiciently forcurrent flow to begin through the windings 9 producing theabove-mentioned transverse magnetic field, the voltage on controlelectrode I is made just sufficient to produce a spot of a desiredluminous intensity on the screen 3. Since the current though the magnetsystem 9 is then substantially zero, the luminous spot is the exactcenter of screen 3. As the voltage curve represented in Fig. 1 risesalong the uniformly increasing portion thereof, the abovementionedmagnetic field so deflects the electron beam as to move the luminousspot radially outward on the screen 3; at the same time the risingpotential of control electrode 28 causes such an increase in the gain ofthe tube 29 that input signals of a given amplitude impressed acrossterminals 253I give progressively greater positive potential on thecontrol electrode 1 as to progressively increase the intensity of theluminous spot on screen 3. This increase in intensity in the luminousspot continues throughout its radial deflection and by proper adjustmentof the tap point by which the capacitor 38 is connected to a resistorI5, this increase in gain of the tube 29 with the resultant greaterintensification for a given input signal may be made substantiallyproportional to the radial deflection of the luminous spot. The luminousspot arrives at the periphery of the screen 3 at the time the voltagerepresented in Fig. 1 reaches the maximum point on the curve. Thisvoltage rapidly drops to its initial value and correspondingly thevoltage on the contro1 electrode 28 of tube 29 is reduced and the gainof tube 29 is also reduced. This reduces the potential swing of controlelectrode 1 for the given amplitude of input signal to so small a valuethat the electrons striking screen 3 do not render the latter luminous.Due to the inherent self inductance of the magnet system 9, theintensity of the deflecting field cannot instantly fall to zero but itrapidly decreases until it reaches the zero value. The electron beamdoes not, however, produce a visible return path to the center of thescreen 3 because, as previously stated, the control electrode 1 has suchlow-voltage swings impressed upon it by the tube 29 when the voltage ofcontrol electrode 28 is impressed with the voltage of the wavetrough inFig. 2 that it prevents any electrons from reaching the screen 3 withsuificient velocityto render the latter luminous.

The above-mentioned events consume one cycle of the wave represented bythe curve in Fig. 2.

While I have illustrated the principles of my invention by showing theirapplication in a particular embodiment thereof, it will be evident tothose skilled in the art that these principles are of broaderapplication in ways which are evident.

I claim as my invention:

1. In combination, a cathode ray tube comprising a luminous screen, anelectron-gun adapted to project an electron stream on a concentratedspot on said screen, a deflector for said electron.

stream adapted to deflect it along a radius of said screen, means forangularly rotating the direction of said radius about a central point ofsaid screen to trace overlapping paths thereon, and means for varyingthe intensity of said electron stream proportionally with its radialdeflection from the center of said screen.

2. In combination, with a cathode ray tube having a luminous screen atone end thereof and an electron-gun for projecting a concentrated beamof electrons into incidence with said screen, a control electrode forvarying the energy with which said electron beams strike said screen,means for deflecting said beam along a radius of said screen, means forrotating the direction of said radius about the center of said screen,means for generating a saw-toothed voltage, means for impressing saidsaw-toothed voltage on said deflecting means, an electrical inputcircuit, means for connecting said input circuit to said controlelectrode and means for impressing a voltage derived from saidsaw-toothed voltage on said control electrode.

3. In combination with a cathode ray tube having a luminous screen atone end thereof and an electron-gun for projecting a concentrated beamof electrons into incidence with said screen, a control electrode forvarying the energy with which said electron beams strike said screen,means for deflecting said beam along a radius of said screen, means forrotating the direction of said radius about the center of said screen,means for generating a saw-toothed voltage, means for impressing saidsaw-toothed voltage on said deflecting means, an electrical inputcircuit, means for connecting said input circuit to an amplifier tubehaving an output circuit voltage impressed on said control electrode andmeans for Varying the current in said output circuit in response to saidsaw-toothed voltage.

GEORGE W. NAGEL.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,234,830 Norton Mar. 11, 19412,121,359 Luck et al June 21, 1938 2,092,081 McLennan Sept. '7, 19372,241,809 De Forest May 13,1941 2,313,966 Pooh Mar. 16, 1943 2,312,761Hershberger Mar. 2, 1943 2,197,900 Schlesinger Apr. 23, 1940 FOREIGNPATENTS Number Country Date 542,634 British Jan. 21, 1942 107,213Australian Apr. 17, 1939 Disclaimer 2,416,199.Ge0rge W. Nagel,Baltimore, Md. CATHODE-RAT TUBE Wrm Spo'r INTENSITY PROPORTIONAL '1'0RADIAL DEFLECTION. Patent dated Feb. 18, 1947. Disclaimer filed May 27,1949, by the assignee, Westinghouse Electric Corporation. Hereby entersthis disclaimer to claim 1 in said patent.

[Oflicial Gazette June 28, 1949.]

Disclaimer 2,416,1995-George W. Nagel, Baltimore, Md. OATHODE-RAY TUBEWrrn Sm'r INTENSITY PROPORTIONAL T0 RADIAL DEFLECTION. Patent dated Feb.18, 1947. Disclaimer filed' May 27, 1949, by the assignee, WestinghouseElectric Corporation. Hereb enters this disclaimer to claim 1 in saidpatent.

Q ficial Gazette June 28, 1.949.]

